That napkin is now known as the ‘Sudarium of Olviedo’.
The marks on the Sudarium match the marks on the facial part of the Shroud in exact detail.
I have to disagree about "perfect detail" since it doesn't match perfectly. The Sudarium does not have an image on it but the blood stains on both the Shroud and the Sudarium do match as to locations and size. There are more than 75 points of congruity between the two cloths and these are more than enough to show a relationship. Fingerprinting require only 8 points of congruity (although their detail is better) for identification. There is enough on the Sudarium to indicate these two cloths were in contact with the same body during the same event.